The inner Solar System showing the distribution of planets and minor bodies. The doughnut-shaped ring of white dots is the asteroid or main belt. Other asteroid groupings (Greeks, Trojans and Hildas) are also shown. Image: Wikipedia
The asteroid belt is found roughly between the orbits of Jupiter and Mars and contains a vast number of generally irregularly-shaped bodies known as asteroids. The four largest bodies in the belt: Ceres, Vesta, Pallas and Hygiea represent about half its mass. Despite the large number of asteroids within the belt, its total mass is only about 4% that of the Moon. It is thought that early in its history approximately 99% of its mass was lost due to the influence of Jupiter, the largest planet in the Solar System. The asteroid belt is the original source of most meteorites that arrive on Earth, with meteorites from Mars and the Moon being notable exceptions.